The present invention concerns an optoelectronic film arrangement, in particular an electroluminescence (EL) film, in accordance with the preamble of the main claim.
Such devices are of general known art from the prior art, and by virtue of their advantageous planar lighting properties in conjunction with low power consumption and extended lighting times, are deployed in a very wide variety of application fields, primarily in the implementation of warning or message surfaces in lighting, advertising, design and architecture.
Planar, film-type electroluminescence devices are based on the functional principle that a so-called active layer, typically consisting of doped zinc sulphide as an electroluminescent material, and a dielectric layer, are provided between two planar electrodes in the manner of a plate condenser, and that this arrangement, when powered by an alternating voltage signal (with a typical frequency between approx. 200 Hz and 4 kHz) emits a cold, planar and non-directional light. The amplitude and frequency of the applied alternating voltage can alter the brightness (and, within limits, also the colour) of the light emission.
In the constructional implementation EL film arrangements of known prior art in accordance with the preamble of the main claim typically have, as a first electrode, a polymer substrate, which is coated with indium tin oxide (ITO), as an implementation of a translucent conductive oxide (TCO), typically by means of vacuum sputtering, such that a conducting, but nevertheless translucent electrode layer is formed. On this coating is provided an active layer of an electroluminescent material, to form a similarly planar and typically non-translucent counter-electrode, implemented, for example, by means of a circuit board; the active layer typically uses zinc sulphide, which is doped with suitable metals such as gold, silver, copper, gallium, or manganese. A dielectric layer, for example, barium titanate, applied to the active layer, prevents a short-circuit between the electrodes, if the (typically non-translucent) counter-electrode complements the generic film arrangement of known art.
From the prior art it is also of known art to apply the active layer and/or the dielectric layer by means of a screen printing method, wherein suitable coating materials provided in the form of pastes for screen printing are commercially available and are provided, for example, by manufacturers such as DuPont.
In particular in the mass production of optoelectronic film arrangements of this kind the transparent ITO-PET front electrode is found to be cost-critical, and in addition is fragile. ITO must furthermore be applied as a very thin coating in order to be sufficiently optically transparent; as a result the electrical conductivity in turn suffers (and thus is typically more than 50 Ω/sq, and therefore has electrical resistance properties that are not insignificant). From this a number of disadvantages in turn ensue: Firstly, items of lighting equipment based on ITO require a power rail, i.e. a connecting rail (typically implemented in terms of silver or silver print) in order to ensure the electrical connection. Thus one dimension of the product is already defined at this point in time, so that, for example, a continuous, endless manufacturing process (with the corresponding cost and quantity advantages) is ruled out. Also these geometrical specifications result in a problem of restricted dimensions with which an even brightness is achieved, and a maximum cut-off frequency for activation is limited by the structure as described.
Accordingly there exists the need for alternative, mechanically improved materials that are potentially cost-effective (but nevertheless enable implementation of a transparent planar electrode), and which, moreover, have improved electrical, i.e. resistance, properties, and less demanding contact requirements.